The focus of this protocol is the identification of genes whose genetic variation predisposes individuals to late-onset NIDDM. It involves the typing of highly polymorphic DNA markers in pairs of affected siblings and in pedigrees in order to identify and localize NIDDM-susceptibility genes. In this protocol we seek to collect genetic material and demographic, historical and physical examination data on 50 multiplex families with NIDDM. Genetic material collected from patients participating in GCRC protocol 6858 will also be analyzed under this protocol.